Caracteristiques physico-chimiques et capacite de charge complementaire du complexe lagunaire Toho-Todougba (sud-ouest, Benin)

La détermination de la capacité de charge est établie pour permettre une utilisation durable des écosystèmes aquatiques tout en maximisant le profit par rapport à la production aquacole. L’objectif de cette étude est de déterminer la capacité de charge en poisson, du complexe lagunaire Toho-Todougba surtout du fait qu’il fait déjà l’objet d’une exploitation intense de production aquacole sans qu’aucune étude préalable n’ait été effectuée. En effet, la concentration en phosphore ainsi que les paramètres hydrologiques et hydrobiologiques ont été mesurées pendant douze mois. La variation spatio-temporelle des paramètres physico-chimiques a été présentée et la capacité de charge a été déterminée en suivant la méthode de Dillon et Rigler (1974). Il en résulte que les paramètres physicochimiques sont recommandables pour les ressources halieutiques malgré les variations constatées par endroit. La capacité de charge déterminée pour la production de tilapia est de 7315,9413 t.an-1. Cependant, cette capacité est de loin ce qui est supportable par l’écosystème puisqu’on considère que le niveau actuel de production est zéro alors que des centaines de cages sont déjà en production. En conséquence, d’autres pisciculteurs peuvent installer leurs unités de production sur le complexe tout en ayant comme référence infranchissable la capacité de charge déterminée.  English title: Physico-chemical characteristics and complementary carrying capacity of the lagoon complex Toho-Todougba (south-west, Benin) The determination of the carrying capacity is established by Dillon and Rigler to allow a sustainable use of the aquatic ecosystems while drawing the maximum profit from the aquaculture production. The objective of this study is to determine the fish carrying capacity of the Toho-Todougba lagoon complex, especially since it is increasingly being intensively exploited for aquaculture production without any prior study having been conducted. Indeed, the phosphorus concentration of the ecosystem was measured during twelve months as well as the hydrological and hydrobiological parameters. The spatio-temporal variation of the physico-chemical parameters was presented and the carrying capacity was determined following the method of Dillon and Rigler. The result is that the physico-chemical parameters are viable for the fishery resources despite the variations observed in some places. The carrying capacity determined for tilapia production is 7315.9413 tons.year-1. However, this capacity is by far what is sustainable for the ecosystem since the current level of production is considered to be zero while hundreds of cages are already in production on the lagoon. Consequently, other fish farmers can install their production units on the complex for fish production while having as an impassable reference the determined carrying capacity. Keywords: Load capacity, Toho-Todougba lagoon, Dillon and Rigler, Beni

Improvement of fish production in Benin: Which strain of Tilapia Oreochromis niloticus is recommended to fish farmers?

Controversies on the performance of the tilapia strain Oreochromis niloticus (S2 INRAB, SI), led us to be interested to the evaluating of that strain’s growth in comparison with the strain commonly used by the fish farmers named Faizou’s strain (SF). Fry of average weight 10.17±2.0663 g were stocked in concrete tank (density: 10 individuals/m2). The experiment lasted 60 days where the temperature, oxygen-dissolved and pH parameters were measured morning and evening every 48 hours. The feed used was made from local products at protein level of 45%. The results revealed that physicochemical parameters have no negative influenced on fish growth even though they were significantly different from one strain to another. The gain in weight obtained was significantly higher for the strain SF (38.12±5.65 g) than the SI (37.15±4.99 g) despite it recorded 13.33% more mortality than the SI strain. Above of this, the average daily gain (ADG) of the SF strain was almost linear over the entire study period, unlike the SI strain whose has no linear ADG. It shows that the SF strain is more productive despite the recorded mortality. This confirms the fish farmers’ claims on the lowest growth of the SI strain, which however is to be considered in selection and breeding programmes

Use of electrochemical impedance spectroscopy to assess the stability of the anion exchange membrane MA-41, modified by poly-N,N-diallylmorpholine bromide in overlimiting current modes

The paper presents the results of studying the electrochemical characteristics and long-term stability of MA-41 membranes on the surface of which poly-N,N-diallylmorpholinium bromide was applied. The deposition of a polyelectrolyte on the membrane surface leads to an increase in the limiting current from 0.8 to 1.1 mA/cm2. The comparison of the experimental and theoretically calculated values of the limiting current density allows us to conclude that the modification of the membrane surface by poly-N,N-diallylmorpholinium bromide does not lead to the formation of a continuous polyelectrolyte film on the surface, but its fixation occurs due to the sorption of macromolecules on the surface of the ion-exchanger particles. To quantify the rate of the water dissociation reaction at the membrane/solution interface, the method of electrochemical impedance was used, which makes it possible to compare the rate constants of the water dissociation reaction for different membranes, assuming that the reaction is described by the Gericher impedance. It is shown that modification of the MA-41 membrane surface leads to a decrease in the rate of the water dissociation reaction in the current range i = 1.5–4ilim by a factor of 2–6. The reduction in water dissociation reaction rate is attributed to the substitution of catalytically active secondary and tertiary amino groups in the surface layer of the pristine membrane by stable heterocyclic ammonium bases of poly-N,N-diallylmorpholinium. The study of the long-term stability of the resulting membrane showed that when the membrane is polarized with a current equal to  twice the limiting current, the desorption of the modifier occurs within 25 h, and the properties of the membrane become close to those of the unmodified MA-41 membrane. It was shown that the electrochemical impedance method can be used as a very sensitive method for studying the long-term stability of ion-exchange membranes

Ecological status of a West African lagoon complex under anthropogenic pressure, Toho-Todougba complex, Benin

Management and preservation of aquatic environments are essential for their productivity and the maintenance of aquatic life. This study aims to characterize the trophic state of Toho-Todougba lagoon complex which has been subject for several years, to an intense fish production in cages. For this purpose, physico-chemical parameters were measured from June 2019 to May 2020 as well as chlorophyll-α, phosphorus and nitrogen. The trophic characterization indices were calculated basedo n Carlson (1977), Burns and Bryers (2000), Neverova-Dziopak and Kowalewski (2018), Primpas et al. (2010) and CCME-WQI (2001). It appears that the temperature (29°C), dissolved oxygen (3.19 mg.L-1 to 4.33 mg.L-1) and pH (6.66 to 7.31) are those characteristic of tropical lake environments. The production parameters revealed that the chlorophyll-α concentration varies from 0.19 to 37 mg.L-1 (stations and months combined). The concentration of phosphorus ranged from 0.02 to 0.42 mg.L-1 while nitrogen varied from 1.91 to 4.03 mg.L-1. Only nitrogen is not in critical proportion for the ecosystem. It should be noted that with the exception of the Carlson index, all other indices revealed that the ecosystem is in a state of advanced eutrophication with a tendency to hyper-trophication according to the eutrophication index of Primpas et al. (2010). Consequently, Toho-Todougba lagoon complex is eutrophic and requires adequate measures for its restoration despite its good health revealed by the physico-chemical parameters

Using a microheterogeneous model to assess the applicability of ion-exchange membranes in the process of reverse electrodialysis

Received: 30.03.2021. Revised: 28.04.2021. Accepted: 30.04.2021. Available online: 30.04.2021.This paper shows the possibility of using a microheterogeneous model to describe the properties of ion-exchange membranes and calculate the characteristics of a reverse electrodialyzer from the data obtained. We studied the properties of eight samples of heterogeneous cation exchange membranes (two samples of each type of membrane). The samples differed in the year of issue and storage conditions. It is shown that for heterogeneous ion-exchange membranes MK-40 and MA-41, the samples' properties can differ significantly. The counterions transport numbers calculated within the framework of the microheterogeneous model for Ralex membranes differ insignificantly. The counterion transport number in 1 mol/L sodium chloride solution is 0.96 for Ralex CM and 0.98 ± 0.01 for Ralex AMH. For the MK-40 membrane, the transport number in the same solution is 0.94 ± 0.04, and for the MA-41 membrane, it is 0.85 ± 0.1. The possibility of calculating the transport numbers and predicting the open-circuit voltage based on simple physicochemical measurements allows selecting the best membrane pairs for the reverse electrodialysis process. Comparison of the open-circuit potential value calculated using the obtained transfer numbers with experimental data showed that in the case of using Ralex membranes, the difference between the experimental and calculated values is 2%. The calculated value of the open circuit potential was 0.19 V/membrane pair or 1.69 V for the investigated reverse electrodialyzer with nine pair chambers.The research was carried out with the financial support of the Kuban science Foundation in the framework of the scientific project № IFR-20.1/110

Removal of Excess Alkali from Sodium Naphthenate Solution by Electrodialysis Using Bilayer Membranes for Subsequent Conversion to Naphthenic Acids

The processing of solutions containing sodium salts of naphthenic acids (sodium naphthenate) is in high demand due to the high value of the latter. Such solutions usually include an excessive amount of alkali and a pH of around 13. Bipolar electrodialysis can convert sodium naphthenates into naphthenic acids; however, until pH 6.5, the naphthenic acids are not released from the solution. The primary process leading to a decrease in pH is the removal of excess alkali that implies that some part of electricity is wasted. In this work, we propose a technique for the surface modification of anion-exchange membranes with sulfonated polyetheretherketone, with the formation of bilayer membranes that are resistant to poisoning by the naphthenate anions. We investigated the electrochemical properties of the obtained membranes and their efficiency in a laboratory electrodialyzer. Modified membranes have better electrical conductivity, a high current efficiency for hydroxyl ions, and a low tendency to poisoning than the commercial membrane MA-41. We propose that the primary current carrier is the hydroxyl ion in both electromembrane systems with the MA-41 and MA-41M membranes. At the same time, for the modified MA-41M membrane, the concentration of hydroxyl ions in the anion-exchanger phase is higher than in the MA-41 membrane, which leads to almost five-fold higher values of the specific permeability coefficient. The MA-41M membranes are resistant to poisoning by naphthenic acids anions during at least six cycles of processing of the sodium naphthenate solution

Electrodialysis Desalination with Simultaneous pH Adjustment Using Bilayer and Bipolar Membranes, Modeling and Experiment

A kinetic model of the bipolar electrodialysis process with a two-chamber unit cell formed by a bilayer (bipolar or asymmetric bipolar) and cation-exchange membrane is proposed. The model allows describing various processes: pH adjustment of strong electrolyte solutions, the conversion of a salt of a weak acid, pH adjustment of a mixture of strong and weak electrolytes. The model considers the non-ideal selectivity of the bilayer membrane, as well as the competitive transfer of cations (hydrogen and sodium ions) through the cation-exchange membrane. Analytical expressions are obtained that describe the kinetic dependences of pH and concentration of ionic components in the desalination (acidification) compartment for various cases. Comparison of experimental data with calculations results show a good qualitative and, in some cases, quantitative agreement between experimental and calculated data. The model can be used to predict the performance of small bipolar membrane electrodialysis modules designed for pH adjustment processes

Etat des ressources naturelles de Djegbadji et de Adounko (Site Ramsar 1017) au sud-ouest Benin (Afrique de l’Ouest) dans le contexte actuel de changement climatique

La préservation des sites Ramsar reste une obligation des pays contractants et nécessite un suivi permanent. Cette étude vise à apprécier l’état actuel des zones de Djègbadji et Adounko au Bénin dans le contexte de changement climatique. A cet effet, 8 placeaux de 900 m2 chacun ont été installés sur deux sites (Adounko et Djègbadji) à raison de 4 placeaux par site. Au sein de chaque placeau, 9 placettes de 100 m2 ont été installées. L’estimation de l’abondance-dominance des espèces recensées a été effectuée. Ensuite, les données satellitaires de la zone d’étude ont été consultées pour une étude comparative entre la période de 2000 à 2016. A l’issue de cette étude, 23 espèces végétales ont été inventoriées avec une dominance significative des espèces de la mangrove (p < 0,05). Au niveau de la faune aviaire, 15 espèces ont été inventoriées avec une abondance plus élevée de Spilopelia senegalensis et Egretta intermedia alors que 8 espèces d’insectes ont été inventoriées avec une abondance plus élevée de Formica sanguinea et Anophele gambiae. Les données satellitaires révèlent que la mangrove et les formations marécageuses ont connu une réduction respective de 1,93% et de 14,77% alors que l’occupation des superficies par les agglomérations a connu une augmentation de 8,32%. Adounko semble être plus préservé que Djègbadji. Mais la dynamique de la biodiversité des deux sites est fortement influencée par les activités anthropiques, ce qui augmente le réchauffement climatique. Des actions fortes de cogestion (décideurs politiques, ONGs et utilisateurs) sont nécessaires pour la préservation.Mots clés: diversité biologique, zone côtière, facteurs anthropiques, BéninEnglish Title: Current state of the natural resources of Djègbadji and Adounko (Site Ramsar 1017) in south west Benin (west Africa) in the climatic change contextEnglish AbstractThe preservation of the biological diversity of Ramsar sites remains an obligation for all contracting countries and requires a permanent follow-up. This was the reason  why the current study was undertaken aiming to assess the current status of the diversity of the coastal zone. Therefore, eight portions of 900 m2 each were identified in two stations at the rate of four per station. Within each portion, nine sub-portions of 100 m2 were set. The abundance-dominance of species was assessed. From the two stations, the study revealed 23 floristic species distributed in 16 families with a predominance of mangrove swamp species (p<0.05). In the avian fauna, a total of 15 species of 11 families were recorded with a predominance of Spilopelia senegalensis and Egretta intermedia. As for insects, 8 species from 7 families were recorded where the most abundant species were Formica sanguinea and Anophele gambiae. The satellite data reveal that the marshy mangrove and formations known a respective reduction of 1.93% and 14.77% whereas the occupation of the surfaces by the agglomerations known an increase of 8.32%. The dynamics of the biodiversity of the two sites is strongly influenced by a number of anthropics activities. It comes out that the biological diversity of the coastal zone is threatened and requires serious actions of co-management from all stakeholders including decision-makers, NGOs and the users of the zoneKeywords: biodiversity, coastal zone, anthropic factors, Beni

An approach to increase the permselectivity and mono-valent ion selectivity of cation-exchange membranes by introduction of amorphous zirconium phosphate nanoparticles

International audienceThis paper addresses hybrid ion exchange membranes fabricated by the synthesis of amorphous zirconiumphosphate (dopant contents from 0.5 to 24 wt%) directly in the pore and channel system of heterogeneouscation-exchange membrane RALEX® CM (by in situ technique). The incorporation of zirconium phosphate nanoparticlesinto the membrane system of pores and channels leads to the displacement of the pore water. As aresult, the cation transport numbers increase. The hybrid materials thus obtained are characterized by increasedionic resistance and enhanced monovalent ion selectivity. The former effect was eliminated by fabrication of asurface-modified membrane. The relative simplicity of modification, together with the benefits of the hybridmaterials make them promising for some membrane processes. Using 31P MAS NMR and elemental analysis,considerable difference between the zirconium phosphate composition inside and outside the membrane wasfound

Improvement of Selectivity of RALEX-CM Membranes via Modification by Ceria with a Functionalized Surface

Ion exchange membranes are widely used for water treatment and ion separation by electrodialysis. One of the ways to increase the efficiency of industrial membranes is their modification with various dopants. To improve the membrane permselectivity, a simple strategy of the membrane surface modification was proposed. Heterogeneous RALEX-CM membranes were surface-modified by ceria with a phosphate-functionalized surface. Despite a decrease in ionic conductivity of the prepared composite membranes, their cation transport numbers slightly increase. Moreover, the modified membranes show a threefold increase in Ca2+/Na+ permselectivity (from 2.1 to 6.1) at low current densities